Detailed Solutions 📝

Explanation: Sponges possess a unique water transport or canal system. Water enters through minute pores (ostia) into a central cavity (spongocoel) and exits via the osculum. This continuous flow of water is essential for food gathering, respiratory exchange, and removal of metabolic wastes. They exhibit strictly intracellular digestion and completely lack a nervous system.

Explanation: In primary succession on bare rocks, lichens are the pioneer species. They secrete acids that dissolve the rock, aiding in weathering and soil formation. This creates a thin layer of soil, paving the way for the next seral stage (bryophytes like mosses).

Explanation: Areolar tissue is a type of loose connective tissue widely distributed beneath the skin, acting as a support framework for epithelium. Tendons and ligaments are dense regular connective tissues, while the skin contains dense irregular connective tissue.

Explanation: Ringworm is one of the most common infectious diseases in humans. It is caused by various pathogenic fungi belonging to the genera Microsporum, Trichophyton, and Epidermophyton.

Explanation: Unlike angiosperms, where the endosperm is triploid (3n) and formed after double fertilization, the endosperm in gymnosperms is actually the cellular haploid (n) female gametophyte itself, which forms before fertilization and acts as a nutritive tissue.

Explanation: DNA polymerase only adds nucleotides in the $5' \rightarrow 3'$ direction. Therefore, on the template strand with $3' \rightarrow 5'$ polarity, replication is continuous (leading strand). On the other template strand with $5' \rightarrow 3'$ polarity, replication is discontinuous (lagging strand), forming Okazaki fragments.

Explanation: Fatty acids and glycerol are insoluble and cannot be absorbed directly into blood. Bile salts first incorporate them into small droplets called micelles in the intestinal lumen. These enter the intestinal mucosa (enterocytes), where they are re-formed into protein-coated fat globules called chylomicrons, which are finally transported into the lymph vessels (lacteals).

Explanation: The nucleolus is a spherical, non-membrane-bound structure present within the nucleoplasm of the nucleus. According to NCERT, it is the active site for the synthesis of ribosomal RNA (rRNA).

Explanation: Lactational amenorrhea relies on the fact that ovulation and the menstrual cycle do not occur during the period of intense lactation following childbirth (effective up to ~6 months). This physiological suppression is mediated by high prolactin levels, which inhibit GnRH and subsequent gonadotropin release, halting the ovarian cycle.

Explanation: Assertion is true: Industrial melanism is a classic case of directional selection where the environment favored the dark phenotype. Reason is false: The soot did not cause a mutation. The dark (melanic) trait was already present as a pre-existing genetic variation in the population. The soot simply changed the background (tree trunks), allowing bird predators to spot and eat the white moths, thereby selecting for the pre-existing dark variants.

Explanation: RNA is functionally dynamic, sometimes catalytic (ribozymes), and structurally labile. Its instability is biochemically attributed to the reactive 2'-OH group on its ribose sugar and the presence of Uracil. DNA, lacking the 2'-OH and possessing Thymine (5-methyluracil), is chemically less reactive and structurally more stable, making it the preferred genetic material.

Explanation: Statement I is false because root pressure is a minor force, only providing a modest push; it cannot lift water up tall trees. Statement II is false because the transpiration pull is a purely physical, passive process relying on the evaporative loss of water and the cohesive/adhesive properties of water molecules; it requires no ATP.

Explanation: Color blindness is an X-linked recessive trait. The man is color-blind ($X^c Y$). The woman has normal vision but her father was color-blind ($X^c Y$), so she must have inherited his $X^c$ chromosome. Thus, she is a carrier ($X^C X^c$). A cross between $X^c Y$ and $X^C X^c$ yields Daughters: $X^C X^c$ (Carrier/Normal) and $X^c X^c$ (Color-blind). Sons: $X^C Y$ (Normal) and $X^c Y$ (Color-blind). Looking only at the daughters, 1 out of 2 possible daughter genotypes is color-blind. Therefore, the probability is 50%.

Explanation: Substrate-level phosphorylation (SLP) refers to the direct enzymatic transfer of a phosphate group to ADP/GDP. During glycolysis (1 glucose), there is a net gain of 2 ATP via SLP. During the TCA cycle (which turns twice for 1 glucose), 2 molecules of GTP (equivalent to ATP) are produced via SLP. Total net ATP via SLP = 2 (Glycolysis) + 2 (TCA) = 4 ATP.

Explanation: A codon consists of 3 nucleotides. To code for 50 amino acids, the mRNA must contain 50 meaningful codons: $50 \times 3 = 150$ nucleotides. Translation termination requires one stop codon (UAA, UAG, or UGA), which does not code for an amino acid but must be present at the end of the sequence: $1 \times 3 = 3$ nucleotides. Total nucleotides = $150 + 3 = 153$.

Explanation: Zygotene: Homologous chromosomes pair up (synapsis) aided by the synaptonemal complex (iii). Pachytene: Recombination nodules appear, and crossing over occurs (ii). Diplotene: Synaptonemal complex dissolves, and X-shaped chiasmata become visible (iv). Diakinesis: Terminalization of chiasmata marks the end of prophase I (i).

Explanation: In a blue-white screen, the vector contains the lacZ gene coding for $\beta$-galactosidase. When a foreign gene is inserted into this sequence, it causes "insertional inactivation." Recombinants lack active $\beta$-galactosidase and cannot break down the chromogenic substrate, remaining white. Non-recombinants have an intact lacZ gene and turn the colonies blue.

Explanation: Elevated T3/T4 indicates hyperthyroidism. The extremely low TSH indicates the anterior pituitary is responding correctly to the negative feedback loop (trying to shut the thyroid down). Because the thyroid is overproducing hormones independent of TSH stimulation (often due to autoimmune antibodies mimicking TSH in Graves' disease), this is primary hyperthyroidism.

Explanation: According to NCERT, the cell-mediated immune response, mediated by T-lymphocytes (specifically cytotoxic T-cells), is primarily responsible for the rejection of transplanted organs. This is why tissue matching and immunosuppressive drugs (like cyclosporin A) are essential.

Explanation: While almost all enzymes are proteins, ribozymes are a notable exception. Ribozymes are catalytic RNA molecules (nucleic acids) that facilitate specific biochemical reactions, such as peptide bond formation (23S rRNA in bacteria).